Theme
Exploring Our Oceans
Oceanography from Space
Biological Science
5.2 Describe interactions between living things and between living things and their non-living surroundings.
6.1 Explain how ecosystems are maintained in terms of energy and matter.
Physical Science
5.1 Describe the characteristics and applications of the transmission and reflection of energy in the form of heat, light and sound.
Background Notes
In order for living things to exist they require energy from the sun to be first trapped by living things like plants. In the ocean away from the coast, where seaweeds can grow attached to rocks and other solid structures, there are no large plants. The only things that can use the sun are tiny drifting plants called phytoplankton.
These tiny plants, which are usually too small to see without a microscope, are responsible for making nearly all the food in the ocean. For the phytoplankton to grow and reproduce easily they require sunlight, carbon dioxide, and certain chemicals called nutrients such as nitrogen, phosphorus, and silicon.
Sunlight is the source of energy for the phytoplankton and is most available in the surface waters of the tropics all year round. At different times of the year different parts of the ocean receive more or less sunlight. In the Northern Hemisphere long hours of sunlight and lots of nutrients in the water result in massive phytoplankton blooms each summer and these rich waters support an extraordinary large number of large marine animals such as whales and fish.
In the Southern Hemisphere we receive more sunlight between December and February than at other times of the year. During our summer the waters of the southern ocean around Antarctica receive long hours of sunlight that allow for the rapid growth of large numbers of phytoplankton.
The phytoplankton are not only important as the start of food webs in the oceans. They are also responsible for producing more than half of the oxygen in our atmosphere and therefore maintain the whole of life, as we know it, on this planet.
Nutrients are chemicals needed by plants for growth. In the oceans these are plentiful where there is water running off the land carrying with it soil and other materials. Nutrients also sink to the bottom of the ocean when marine animals and plants die and their remains are decomposed and sink to the bottom. These nutrients are gradually moved across the ocean basins by deep-water ocean currents. Because there are few nutrients that reach the surface of the middle of the oceans there is little to help phytoplankton to grow.
In some places cold deep water is brought to the surface as upwellings. In such places phytoplankton are able to grow rapidly and provide food for many animals small and large.
As light passes down through the ocean it is absorbed rapidly. Even after only after a few metres red colours cannot be seen because the water absorbs the red part of the visible light spectrum. Most phytoplankton live in the top 100m of water. Only a small amount of light penetrates deeper than this. Beyond 1000 metres depth their is no light at all and living things are generally much less abundant.
Obtain an Phytoplankton Density image of the oceans by going to the NASA SeaWIFS Ocean Images site at http://seawifs.gsfc.nasa.gov/SEAWIFS/CZCS_DATA/global_full.html (Click on the image itself to get a more detailed image)
View sample images here
Activity 1. A Feast of Plankton
Activity 2. Productivity, Biomass and Diversity
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